Weakened Brain Structure May Cause Phantom Limb Sensation

According to a recent study, after a person has limb amputation, the areas of his or her brain responsible for movement and sensation alter their functional communication. The study's authors found two main changes in functional sensorimotor connectivity. One affected communication between the left and right sides of the brain, and the other affected only the side of the brain contralateral to the amputation. The researchers found a "pronounced reduction" in functional connectivity between the two brain hemispheres in the individuals with amputations.

The results represent a step toward understanding brain plasticity and may help explain why some patients report phantom sensations and others do not, according to the study published in February in Scientific Reports.

Scientists at two research centers in Brazil, the D'Or Institute for Research and Education (IDOR) and the Federal University of Rio de Janeiro, investigated the differences in functional connectivity (i.e., the communication of brain areas) among motor and sensitive areas connected by the corpus callosum, the brain structure that connects the left and right cortical areas responsible for movement and sensations. Participants included nine people with long-term traumatic lower-limb amputations who reported phantom sensation but no pain, and nine healthy volunteers.

The researchers used tactile stimulation of the residual limb and the remaining foot and 3T functional magnetic resonance imaging (MRI) to investigate the functional connectivity changes in the sensorimotor network of the participants.

In a previous study from the same group, an MRI experiment revealed that the brain overreacted when the residual limb was touched. They also found that the corpus callosum had weakened. Those findings raised interest in the impact of an impaired corpus callosum on the cortical areas it connects.

"The brain changes in response to amputation have been investigated for years in those patients who report phantom limb pain. However, our findings show that there is a functional imbalance even in the absence of pain in patients reporting only phantom sensations," said Ivanei Bramati, a medical physicist and doctoral student at IDOR and the study's first author.

Editor's note: This story was adapted from materials provided by D'Or Institute for Research and Education.